This invention relates to a fuel-injection device for an internal-combusion engine. The effective nozzle cross section of a fuel-injection device of this type is small during partial-load operation, so that the fuel pressure adjusting itself is great enough to ensure good atomization and an optimal combustion of the fuel. However, during full-load operation the effective injection cross section must be its maximum.
In Swiss Pat. No. 622 588 there is described an injection device of this type in which the fuel delivery to a spray hole in the nozzle body is controllable by a valve needle. A control device having a control edge is displaceably mounted in a bore of the valve needle, which control edge unblocks part of the cross section of the spray hole during partial-load operation of the engine and opens the entire cross section of this spray hole during full-load operation. Thus, in this injection device the fuel is always injected through the same spray hole which is advantageous in some applications. However, it is disadvantageous that the shape of the jet does not solely depend on the shape and the dimensions of the spray hole. Further, during partial-load operation the fuel under high pressure is deflected by the control edge on the control device so that the vorticity will be effected, the result of which is a lower speed of the fuel delivery as it leaves the spray hole. This results in a detoriation of the jet shape and unfavorable combustion action.
This disadvantage is overcomed in an embodiment according to the British Pat. No. 1 593 112. In this embodiment, two spray holes are incorporated in the nozzle body, whereby the fuel delivery to the two spray holes is controllable by a valve needle. A shutoff element is axially displaceably guided in a bore of the valve needle, which shutoff element shuts off one of the two spray holes in the rest position. Thus, during full-load operation in this embodiment, the fuel is injected into the combustion chamber through both spray holes. However, during partial-load operation one spray hole is shut off and the fuel is only injected through the other spray hole. In the embodiment, the jet shape solely depends on the shape and on the dimensions of the spray holes. Thus, this embodiment has the advantage that the high fuel pressure existing on the inlet opening of the spray hole is turned into a high fuel speed alongside the spray hole as far as the outlet opening which is essential for an optimal combustion. However, it is disadvantageous in some applications that in partial-load operations and in full-load operation that the number of the injection jets and their position are different. Furthermore, in this embodiment there is a danger of coking at the spray hole controlled by the control device if the spray hole is shut off for a longer time.
A fuel-injection device is known from German specification OS No. 26 56 276, in which the disadvantage last mentioned has been avoided, wherein during partial-load operation the fuel is conducted through nozzle openings which effect the necessary reduction of the cross section, whereby these nozzle openings are coaxially adjusted to the spray holes in the nozzle body. Thus, in this embodiment the fuel always emerges through the same spray holes both at partial-load operation and at full-load operation. Therefore, there is no danger of coking at these spray holes. However, the complexity of this embodiment is disadvantageous because one valve is required for partial-load operation and another for full-load operation, whereby one fuel channel each is conducted to these valves and the fuel supplied by the pump is selectively delivered to one or the other fuel channel by additional means.
It is a disadvantage of all of these known devices in that the change over from partial-load operation to full-load operation is at least indirectly dependent on the pressure of the fuel supplied. This makes it difficult to determine the switching point at which the nozzle cross section is to be enlarged. This is particularly disadvantageous in internal-combustion engines with several injection nozzles, because due to unavoidable tolerances a uniform and simultaneous change over from the smaller to the larger nozzle cross section cannot be ensured for all injection nozzles. It is furthermore disadvantageous that, as illustrated in the Swiss Pat. No. 622 588, that the control device is also adjusted to each injection and thus it is subject to high loads and increased wear.
The present invention, therefore, addresses the problem of improving a fuel-injection device of the type described in which an optimal combustion of the fuel is achieved including multi-cylinder engine applications, without increased complexity.
The invention is thereby based on the problem of realizing the principle according to the German specifications OS No. 26 56 276 with a single fuel supply channel, that is the operating position of the control device the fuel is directly conducted to the spray hole, but in the rest position of the control device the fuel is conducted to the spray hole only be way of the nozzle opening with the reduced cross section coaxially adjusted thereto. Furthermore, the present invention is based on the finding that a uniform switching behavior of the shutoff elements of several injection nozzles can be achieved, if the adjusting action of these shutoff elements is released by an active actuating element independently of the position of the valve needle and independently of the pressure of the fuel supplied. Because the change over of this control device is independent of the fuel pressure, this control device can be changed over into the respective position before an injection begins, so that in full-load operation the larger nozzle cross section is already effective at the beginning of the injection. It is furthermore advantageous that according to the present invention the position of this control devices remains unchanged for several injections, while in the prior art this control device is adjusted with each injection with a pressure-dependent control.